Humidifier for respiratory apparatus

ABSTRACT

A respiratory apparatus for delivering breathable gas to a patient includes a flow generator that generates a supply of pressurized gas to be delivered to the patient; a humidifier for vaporizing water and delivering water vapor to humidify the gas; a gas flow path leading from the flow generator to the humidifier and from the humidifier to a patient interface; and a heater in thermal contact with the gas and/or the water, wherein the heater includes an elongate heating filament in the form of a tape. A humidifier for respiratory apparatus includes a first respiratory gas passage for receiving gas from a flow generator, a humidifier chamber, a second respiratory gas passage for delivering humidified gas to a patient interface, and a heater in thermal contact with the gas and/or the water, wherein the heater includes an elongate heating filament extending along at least part of both said first and second respiratory gas passages. A conduit for use in a respiratory apparatus for delivering breathable gas to a patient includes a tube; a helical rib on an outer surface of the tube; and a plurality of wires supported by the helical rib in contact with the outer surface of the tube.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application 60/955,222, filedAug. 10, 2007, and to Australian Provisional Application 2006906224,filed Nov. 8, 2006, the entire contents of both of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to humidification and heater arrangementsused to control the humidity of breathable gases used in all forms ofrespiratory apparatus ventilation systems including invasive andnon-invasive ventilation, Continuous Positive Airway Pressure (CPAP),Bi-Level therapy and treatment for sleep disordered breathing (SDB)conditions such as Obstructive Sleep Apnea (OSA), and for various otherrespiratory disorders and diseases.

2. Description of Related Art

Respiratory apparatus commonly have the ability to alter the humidity ofthe breathable gas in order to reduce drying of the patient's airway andconsequent patient discomfort and associated complications. The use of ahumidifier placed between the flow generator and the patient mask,produces humidified gas that minimizes drying of the nasal mucosa andincreases patient airway comfort. In addition in cooler climates, warmair applied generally to the face area in and about the mask, as mayoccur inadvertently by a leak, is more comfortable than cold air.

Many humidifier types are available, although the most convenient formis one that is either integrated with or configured to be coupled to therelevant respiratory apparatus. While passive humidifiers can providesome relief, generally a heated humidifier is required to providesufficient humidity and temperature to the air so that patient will becomfortable. Humidifiers typically comprise a water tub having acapacity of several hundred milliliters, a heating element for heatingthe water in the tub, a control to enable the level of humidification tobe varied, a gas inlet to receive gas from the flow generator, and a gasoutlet adapted to be connected to a patient conduit that delivers thehumidified pressurized gas to the patient's mask.

Typically, the heating element is incorporated in a heater plate whichsits under, and is in thermal contact with, the water tub.

The humidified air may cool on its path along the conduit from thehumidifier to the patient, leading to the phenomenon of “rain-out”, orcondensation, forming on the inside of the conduit. To counter this, itis known to additionally heat the gas being supplied to the patient bymeans of a heated wire circuit inserted into the patient conduit whichsupplies the humidified gas from the humidifier to the patient's mask.Such a system is illustrated in Mosby's Respiratory Care Equipment(7^(th) edition) at page 97.

Such a heating method for the patient conduit may only provide poor heattransfer due to the wire locating itself along the conduit wall ratherthan in the main gas stream. A wire will also only give poor turbulentmixing due to its low profile. As a result heat transfer may be poor andthe mixing of water vapor and gas may also be poor.

Alternatively the heating wire circuit may be located in the wall of thepatient conduit. Such a system is described in U.S. Pat. No. 6,918,389.

U.S. Pat. No. 6,918,389 describes a number of humidifier arrangementsfor supplying low relative humidity, high temperature humidified gas tothe patient. Some of these arrangements include pre- or post-heating ofthe gas to reduce the relative humidity.

None of these prior art devices provides an entirely satisfactorysolution to the provision of comfortable humidified breathable gas tothe patient, nor to ease of construction and hygiene requirements and toenergy and patient comfort requirements at startup.

SUMMARY OF THE INVENTION

Examples of the present invention aim to provide an alternativehumidifier arrangement which overcomes or ameliorates the disadvantagesof the prior art, or at least provides a useful choice.

In one sample embodiment of the invention, a humidifier and/ortemperature or other sensing or control apparatus for use withrespiratory apparatus comprises a heating filament in thermal contactwith the gas and/or water, wherein the filament is in the form of anelongate tape. The tape may be flexible, and may, in a sampleembodiment, be passed along the bore of the patient gas conduit, orincorporated into the conduit wall.

In another sample embodiment, a humidifier for use with respiratoryapparatus comprises a heater in contact with water in the humidifiertub, and which floats or otherwise rises and falls with changes in thewater level in the humidifier tub.

In a further form, the invention provides a humidifier arrangement forrespiratory apparatus, including an elongate filament heater in contactwith the air path in the regions before and after the humidificationchamber. The filament heater may be further in contact with a body ofwater in the humidification chamber.

Heating of the filament may be divided into two or more separatelycontrollable zones.

A further sample embodiment of the invention provides a method ofincreasing patient comfort during start-up of humidification, the methodcomprising providing a heating element to thermally contact breathablegas being provided to the patient along a gas flow path and to thermallycontact water in a humidifier apparatus; and configuring the heatingelement to heat the gas in the gas flow path and to heat the water inthe humidifier apparatus, such the patient is initially provided withheated gas while the temperature of the water in the humidifierapparatus is being increased to its operating temperature.

The heating of the gas in the gas flow path may include heating of apart of the gas flow path upstream of a humidification chamber such thatpassage of the heated gas through the humidifier apparatus provides aninitial degree of humidification.

According to a sample embodiment of the invention, a conduit for use ina respiratory apparatus for delivering breathable gas to a patientcomprises a tube; a helical rib on an outer surface of the tube; and aplurality of wires supported by the helical rib in contact with theouter surface of the tube.

According to another sample embodiment of the invention, the conduit mayfurther comprise a connector block connected to an end of the conduit,wherein the connector block is configured to be connected to a flowgenerator or a patient interface of the respiratory apparatus.

According to a further sample embodiment of the invention, a respiratoryapparatus for delivering breathable gas to a patient, comprises a flowgenerator to generate a supply of pressurised gas to be delivered to thepatient; a humidifier to vaporize water and to deliver water vapor tohumidify the gas; a first gas flow path leading from the flow generatorto the humidifier; and a second gas flow path leading from thehumidifier to a patient interface, wherein the first gas flow pathcomprises a first conduit having a first connector block configured tobe connected to the flow generator and the second gas flow pathcomprises a second conduit having a second connector block configured tobe connected to the patient interface.

According to still another sample embodiment of the invention, a methodof delivering breathable gas to a patient comprises delivering ahumidified flow of breathable gas to a patient interface via a conduit;heating the conduit by supplying a DC current at a predetermined dutycycle to a plurality of wires supported by the conduit; sensing atemperature in the conduit during an OFF cycle of the predetermined dutycycle; and controlling the DC current to maintain the temperature in theconduit at a selected temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1-A is a schematic side sectional view of the patient conduit witha flexible tape heater in an embodiment of the present invention;

FIG. 1-B is an alternative embodiment of FIG. 1-A where the flexibletape heater is in a helical configuration;

FIG. 1-C: is an alternative embodiment of FIG. 1-A where the flexibletape heater is twisted about its longitudinal axis;

FIG. 2 is a schematic perspective view of another embodiment of theflexible tape heater;

FIG. 3 is a schematic side sectional view of the humidification chamberwith an embodiment of the floating heater;

FIG. 4-A-D schematically illustrate a number of embodiments that thefloating heater may have within the humidification chamber;

FIG. 4-A is a side perspective view of an embodiment of the floatingheater, a circular floating plate heater which is secured under afloating plastic support grid;

FIG. 4-B is a side perspective view of another embodiment of a floatingheater;

FIG. 4-C is a perspective side view of another embodiment of a floating,helical flexible tape heater;

FIG. 4-D is a plan view of another embodiment of a flexible tape heaterwound in a horizontal spiral;

FIG. 5 schematically illustrates a humidification heater arrangementcomprising multiple zones;

FIG. 6-A is a transverse cross-sectional view of the patient conduitshowing the flexible tape heater connected to the conduit wall;

FIG. 6-B is another view of the connector embodiment of FIG. 6-A wherethe connector is disengaged;

FIG. 7 illustrates the floating heater plate located in a shallow baththat also floats at the water surface of the body of water;

FIG. 8 illustrates a power supply/controller connected to an inletconduit by a connector according to a sample embodiment of theinvention;

FIG. 9 illustrates the inlet conduit of FIG. 8 connected to a flowgenerator;

FIG. 10 illustrates a patient conduit or hose according to a sampleembodiment of the invention connected to a patient interface;

FIG. 11 illustrates an inlet conduit, including a flow generatorconnector cuff, connected to a connector according to a sampleembodiment of the invention;

FIG. 12 illustrates the inlet conduit of FIG. 11 disconnected from theconnector;

FIG. 13 illustrates a cross section of the inlet conduit and connectorof FIG. 11;

FIG. 14 is a rear perspective view of the inlet conduit and portions ofthe flow generator connector cuff with the terminal clip connectedthereto;

FIG. 15 is a front perspective view of the inlet conduit, flow generatorconnector cuff portions, and terminal clip of FIG. 14;

FIG. 16 is a top perspective view of the inlet conduit and flowgenerator connector cuff portions without the terminal clip;

FIG. 17 is a perspective view of the terminal clip according to a sampleembodiment of the present invention;

FIG. 18 is a perspective view of the connector block of the flowgenerator connector cuff according to a sample embodiment of theinvention;

FIG. 19 is a perspective view of the connector according to a sample ofthe invention;

FIG. 20 is a perspective view of the contacts of the connector of FIG.19;

FIG. 21 is a cross section of the contacts and the connector of FIG. 20;

FIG. 22 is a perspective view of the patient conduit or hose andportions of the mask cuff or connector according to a sample embodimentof the invention;

FIG. 23 is a cross section of the patient conduit and mask cuff of FIG.22 with portions of the cuff removed;

FIG. 24 is a cross section of the patient conduit and mask cuff of FIG.10;

FIG. 25 is a top perspective view of the connector block of the maskcuff according to a sample embodiment of the invention;

FIG. 26 is a bottom perspective view of the connector block of FIG. 25;

FIG. 27 is a top perspective view of the connector block of the maskcuff in connection with the patient conduit and including a printedcircuit board of the mask cuff according to a sample embodiment of theinvention;

FIG. 28 is a side perspective view of the connector block of FIG. 27disconnected from the patient conduit;

FIG. 29 is a cross section of the patient conduit and connector block ofFIG. 27;

FIG. 30 is a perspective view of the patient conduit and the connectorblock of the mask cuff according to a sample embodiment of theinvention;

FIG. 31 is a perspective view of the patient conduit and mask cuffaccording to a sample embodiment of the invention;

FIG. 32 is a cross section of the patient conduit and mask cuff of FIG.31;

FIG. 33 is a schematic illustration of the temperature sensor andthermal fuse of the circuit of the mask cuff according to a sampleembodiment of the invention;

FIG. 34 schematically illustrates the circuit of the mask cuff providedon the connector block of the mask cuff;

FIG. 35 schematically illustrates power supply/controller according to asample embodiment of the present invention;

FIG. 36 schematically illustrates a three wire heated tube according toa sample embodiment of the invention;

FIG. 37a schematically illustrates a sample embodiment of the circuitsof the power supply/controller;

FIGS. 37b -1-37B-4 schematically illustrate a sample embodiment of thecircuit of FIG. 37 a;

FIGS. 38-40 are perspective views of overmolded grip portions for theflow generator cuff and/or mask cuff;

FIG. 41 illustrates a conduit according to a sample embodiment of theinvention;

FIG. 42 illustrates a conduit according to a sample embodiment of theinvention; and

FIG. 43 illustrates a patient conduit and mask cuff according to asample embodiment of the invention.

DETAILED DESCRIPTION

Flexible Tape Heater

FIGS. 1-A to 1-C illustrate the use of a flexible tape heater 3 withinthe patient conduit 4 of a respiratory apparatus. The patient conduit 4is located between the humidification chamber 1 and the patientinterface, e.g. mask 5. The patient conduit 4 conveys the flow of gasfrom the humidification chamber 1 to the patient mask 5 in respiratoryapparatus. The humidification chamber 1 in turn receives pressurized gasfrom a flow generator 20 (FIG. 5) or blower.

The flexible tape heater 3 in the patient conduit 4 is used to heat theflow of gas in the patient conduit 4. Heating of the gas enables the gascomfort features of temperature and humidity to be attained andmaintained for the gas delivered by the respiratory apparatus.

The flexible tape heater 3 is electrically coupled to a heatercontroller 21 (FIG. 5) by a patient conduit connector end 2. The heatercontroller 21 may be incorporated in the humidifier or the flowgenerator 20 or the base unit 22, or be a separate unit 21, for examplesupplying a DC voltage of, for example, 0.1-24V.

The patient conduit connector end 2 may connect to the heater controller21 via another flexible tape heater (partially shown on the left side inFIG. 1) or to the conduit wall 25, of the patient conduit 4, via aconnector 23, 24 shown in FIGS. 6-A and 6-B. The connector may include amale connector element 23 and a female connector element 24 which maymake an electrical, communications and/or mechanical connection betweenthe flexible tape heater 3 and the conduit wall 25. The male connectorelement 23 and the female connector element 24 may be interchangeable inposition. The connector 23, 24 locks the flexible tape heater 3 inposition on the conduit wall 25, but may also be disengaged. Theconnector 23, 24 may be used at any location along or around the conduitwall 25.

The patient conduit 4 may be insulated or a heated conduit as in theprior art in order to reduce heat loss and minimize consequent watercondensation or “rain-out” within the patient conduit 4. The insulationcould be an outer sleeve or wrapping about the patient conduit 4. Theouter sleeve or wrapping could be foam, fabric or an air space in thecase of a double walled conduit.

In another embodiment the flexible tape heater 3 may be combined withthe wall of the patient conduit 4 in order to provide heating to thewall to prevent condensation, while optionally an additional flexibletape heater 3 within the patient conduit 4 provides the heating to thegas flow.

In a further embodiment the patient conduit 4 is formed by making ahelix of the flexible tape heater 3 and joining the edges the flexibletape heater 3 to form the patient conduit 4.

The flexible tape heater 3 should be sufficiently flexible so that inuse flexing of the patient conduit 4 is not restricted. The flexibilityof the flexible tape heater 3 also should be sufficient to enableinsertion and removal of the flexible tape heater 3 within the patientconduit 24, while being sufficiently stiff so that the flexible tapeheater 3 can be inserted into the patient conduit 4 and will supportitself in a desired position and not collapse against a wall or to oneend of the patient conduit 4. Additionally the stiffness should besufficient so that the flexible tape heater 3 will not flutter in thegas stream to produce an unwanted audible noise.

The thin, flat and extended nature of the flexible tape heater 3enhances heat transfer with the gas flow while also providing lowimpedance to the gas flow. The flexible tape heater 3 can be placed inthe patient conduit 4 such that it has a helical configuration (FIG.1-B) and/or the flexible tape heater 3 can be twisted or bent about oneor more of the flexible tape heater 3 axes. The longitudinal axis twistconfiguration is illustrated in FIG. 1-C.

Alternative profiles or geometric structures for the flexible heatingtape may include:

The transverse cross-section of the flexible tape heater may berectangular, elliptical or arbitrary;

The surface of the flexible tape heater 3 may be rough or smooth ordimpled; and/or

One or more surfaces of the flexible tape heater 3 may be rippled.

The dimensions of the thickness and width may vary along the length ofthe flexible tape heater. For example a thicker section of the flexibletape heater 3 in the patient conduit 4 may be provided to give a venturieffect of increasing the gas flow rate so that flow detection may bepossible by pressure sensors along the length of the flexible tapeheater 3.

The use of these twisted, helical or other configurations describedabove increases the length of the flexible tape heater 3 in the patientconduit 4 and thus the available surface area for heat transfer betweenthe gas flow and the surface of the flexible tape heater 3. Additionallythese configurations can be used to enhance the turbulent mixing of thewater vapor produced in humidification chamber 1 with the gas flow.

The various configurations may also be used to provide zones ofdiffering flow, acoustic, humidity or temperature properties along thepatient conduit 4 or the apparatus as a whole, as show in FIG. 5 forexample.

It may be desirable to modify the acoustic impedance properties of thepatient conduit 4 using the flexible tape heater 3. For example:

The generation or reduction in white noise (broad frequency spectrumnoise);

The damping or filtering of a particular acoustic noise frequencycomponent/s, e.g. structure-borne or air-borne flow generator tonalnoise; and/or

Enhancement of the propagation of patient respiratory acoustic signalsthrough the patient conduit 4 and to the base unit 22 (FIG. 5) formonitoring and diagnosis.

The alteration of acoustic impedance properties using the flexible tapeheater 3 may be achieved by the choice of the materials making up theflexible tape heater 3 and the configurations described above of theflexible tape heater 3 in the patient conduit 4, and additionally asshown in FIGS. 1-A to 1-C.

FIG. 2 illustrates one embodiment of the flexible tape heater 3, inwhich the heating is by a heating element 6.

In one embodiment, the heating element 6 is formed by printed circuittechniques applied to a surface of a flexible substrate such as KAPTON®,silicone rubber, all-polyimide, PTFE. Included in the printed circuittechniques which may be used are etched foil, printing and vacuumdeposition techniques.

Another sheet of the substrate material is then laid upon the bottomsubstrate with the heating element and the two sheets of substratematerial adhered or fused together to encapsulate the heating element.The Thermofoil™ range of the type of flexible heaters by Minco ofMinneapolis USA, described at www.minco.com, are examples ofcommercially available strip heaters which may be modified for use inthe present invention.

An alternative embodiment to produce a flexible tape heater 3 is to usea laminator, such as a twin silicon roller laminator, to encapsulate aheating element 6, that is in the form of wire or ribbon, within twotapes of polycarbonate film. The resulting tape may for example havedimensions ranging from 1 to 10 mm wide and 0.1 to 1 mm thick.Dimensions of from about 0.2 to 0.5 mm in thickness and about 5 mm wideare usable in the patient conduit 4.

The heating element 6 wire or ribbon may have any suitable transversecross-section, for example circular, elongate or rectangular. Theheating element 6 may for example consist of a resistive conductor.

The arrangement of the heating element 6 between the laminating filmsmay be any ordered or disordered arrangement that increases the heattransfer of the flexible tape heater 3 to the surrounding media, be itgas or liquid. The heating element 6 may also have a positive thermalcoefficient (PTC) for resistance such that heating decreases as thetemperature increases towards a desired temperature.

Alternatively the heating element 6 may have a negative thermalcoefficient (NTC) to allow sensing of the temperature of the heatingelement 6 or surrounding media.

In other embodiment there may be multiple heating element circuitswithin the flexible tape heater 3. The multiple heating elements may beconnected in series or parallel. The use of these multiple heatingcircuits within a flexible tape heater 3 enables additional heating tobe applied as required in the operation of the respiratory apparatus.

In other embodiments the laminating films may be polyester,polypropylene or any suitable and approved substance for respiratorymedicine use. Alternatively, multiple laminating films may be used tocreate a composite strip having the desired properties while retainingthe desired compatibility of the outer film for respiratory medicineuse. Other conductors may also be present between each of these multiplelayers, for example so as to form multiple heating circuits, such as toallow multiple heating zones along the length of the tape heater.

In another embodiment, a sensor 7 for air temperature, such as athermocouple, platinum resistance thermometer or thermistor with itsattendant signal wires 9, may be included between the two sheets ofpolycarbonate film. The sensor tip may be flat with a thickness of lessthan about 2 mm, and may be less than 1 mm. Other circuit componentssuch as surface mount circuit components may be incorporated onto thesubstrate film for sensing and/or controlling and hence into theflexible tape. Also, the heating element 6 and other circuit componentscan exist in multiple layers separated by substrate films as describedabove.

For the flexible tape heater 3 the other circuit components all have thecommon physical feature that they are of a small enough dimension toenable them to be accommodated in the overall profile of the flexibletape heater 3 and collocated with the heating element 6.

In an alternative embodiment the flexible tape may not have a heaterelement 6, but instead incorporate one or more other circuit componentsfor sensing and controlling. Thus a respiratory apparatus may containtwo or more flexible tapes, one or more undertaking a heating functionand one or more undertaking a sensing and/or controlling function.

The range of other circuit components that may be used is shown by wayof example in the following:

Relative and absolute humidity sensors 7 a;

Temperature sensors 7 a with a positive temperature coefficient (PTC) ornegative temperature coefficient (NTC) in the form of a thermistor oralternatively the PTC property may be intrinsic to the heating element 6so that the flexible tape heater 3 is self limiting;

Thermocouples, platinum resistance thermometers and the like may be usedto produce an actual temperature value signal for control andmonitoring;

Directional flow sensing of the gas may realized by using at least twoindependently controlled heating sections spaced along the flexible tapeheater each comprising a temperature sensor (e.g. thermistor). The twoor more heating sections are controlled and the temperatures sensed todetect the direction of gas flow;

Hot wire anemometry for gas flow sensing 7 a;

Ambient pressure sensing 7 a, e.g. inspiratory versus expiratorypressures;

Controller 7 b that makes use of the output from a sensor 7 a, such asfor temperature, to control, for example, a transistor which regulatesthe current applied to a heating element 6 used for the heatingelement(s);

Identification-Communication-Memory chips 8 which enable identificationand communication of the operating parameters of the flexible tapeheater 3 to the base unit 22, other heaters and components in therespiratory apparatus. For example, the flexible tape heater 3 maycommunicate regarding itself as well as detect and report regardingother components that are attached to the respiratory apparatus such asthe patient mask 5 type or the patient conduit 4 type or an active ventsystem. The information thus gathered by the flexible tape heater 3 maythen be sent to the base unit 22. Theidentification-communication-memory system may consist of in part aradio frequency identification chip (RFID) to store the heater 6 andsensor 7 a identification and operating parameters. The base unit 22 mayhave a capability to communicate with the RFID chip and adjust itsoperation accordingly. Such a system has been described in theAustralian Patent Application No. 2005907200, titled “IdentificationSystem and Method for Mask and Ventilator Components,” the entirecontents of which are incorporated herein by reference. Thecommunication may also be used to control an active vent system;

Electromagnetic communication protocols via miniature aerials andreceivers, e.g. “Bluetooth.”. Aerials for transmitting and receivinginformation may be located for example in the flexible tape heater 3,the wall of the patient conduit 4, or an active vent system, or withinthe other components of the respiratory apparatus as illustrated in FIG.5. In another embodiment the aerials could be of a dimension as allowedby the length of the flexible tape heater 3 or the patient conduit 4;

Power supply to the flexible tape heaters may be in a similar manner tothe electromagnetic communication described above. In this embodimentthe aerials or inductive coils would be adapted for power transmission.

These components can be located anywhere along the flexible tape heater3 as appropriate to their function. For example, a thermocouple may belocated on the flexible tape heater 3 at the end adjacent the patientmask 5 to enable closed loop temperature control based on gastemperature delivered to the patient mask 5.

In an alternative embodiment the temperature sensor may be located in orin the vicinity of the patient mask 5 but separated from the flexibletape heater 3. However the temperature sensor may communicate with theflexible tape heater 3 in the one of the manners described above toenable closed loop control of the temperature of the gas delivered tothe patient.

The flexible tape heater 3 may also comprise microtubes 26 (FIG. 2) toallow remote sensing away from the flow generator and/or humidificationchamber 1. The microtubes may, for example, provide pressure,noise/snore and/or cardiological signal sensing. For example, themicrotubes may be attached to the side of the flexible tape heater 3 andconnected back to the flow generator 20 in one of the manners describedabove. The use of microtubes 26 provides the benefit of avoiding flownoise within the patient conduit 4 and other areas in the respiratoryapparatus.

The sensing and control methods described above allow closed loopcontrol to be used for improving gas delivery to the patient mask 5 sothat it is at the desired temperature and humidity. Alternatively, asimple open loop system may be used where driving voltages or currentsfor the heating element may be, for example, from 0.1 to 24 V directcurrent or the power equivalent for alternating current, that may forexample be from 0.1 to 50 W. The sensing and control may also controlthe level of intentional gas leak from an active vent system, dependingon the amount of pressure being supplied. For example, as the ventilatorpressure increases the active vent system may be controlled to reducethe level of its intentional leak to an acceptable level.

Additionally, the sensors 7 a can be used for compliance or statisticaldata gathering.

Furthermore, the different components of the heater and/orsensing/control system described herein may be used as stand alonecomponents in a respiratory apparatus not employing a humidifier, andsuch arrangements are within the scope of the invention.

A flexible tape heater 3 as thus described would be easily removablefrom the patient conduit 4 to enable cleaning, maintenance orreplacement. The flexible tape heater 3 also offers efficient heatingwith sensing and control components 7 being easily incorporated into theflexible tape heater 3.

Floating Heater

In FIG. 3 a humidifier arrangement utilizing a floating heater 12 isillustrated. The floating heater 12 floats in the body of water 13 inthe humidifier chamber tub 1 such that a substantial portion of thefloating heater 12 is immersed but is still adjacent to the watersurface 14 so as to heat that part of the water near the surface 14.

The floating heater 12 may comprise a length of flexible tape heater ofsimilar construction to that discussed above with reference to FIGS. 1-Ato 1-C and 2. The end of the heater located in the inlet conduit 10leading from the flow generator 20 may be provided with a connector 11which enables the floating heater 12 to connect with a flexible tapeheater, where that flexible tape heater is connected to the base unit 22(FIG. 5) of the respiratory apparatus. The floating heater 12 receivesits electrical supply via the upstream end connector 11. Any sensing orcontrolling signals to or from the floating heater 12 are also receivedvia the upstream end connector 11.

The downstream end 2 of the floating heater, located in the patientconduit 4 leading to the patient interface, may have a further connectorfor supplying power and any communication with a further portion offlexible tape heater located in the patient conduit 4 (see FIGS. 1-A,1-B, 1-C and 2).

The heater 12 may be adapted to float either by the natural buoyancy ofthe heater itself, by surface tension effects, or may be supported in amanner which keeps the heater near the water surface regardless ofchanges in the water level.

FIG. 4-A-E illustrate a number of embodiments that the floating heater3, 12, 16, 17 may have within the humidification chamber 1. The floatingheater 3, 12, 16, 17 in each embodiment is formed either from a flexibletape heater of the type previously described or a plate form of theflexible tape heater 3, the floating plate heater 16.

The construction and use of a floating flexible tape heater 3 and thefloating plate heater 16 is the same as described for the flexible tapeheater 3 above, except that it is applied to water. This has thesignificant advantage that the heater for both applications is robust togas or water immersion, since a floating flexible tape heater 3 or afloating plate heater 16 could be partially immersed in water during therespiratory apparatus' operation, either unintentionally as the body ofwater increases or decreases in volume or by tilting of the device, orintentionally to maintain the temperature of the water vapor in the gasof the humidification chamber 1.

FIG. 4-A illustrates a circular floating plate heater 16 which issecured under a floating support grid or plate 15, for example of abuoyant plastics material. The support grid 15 provides a floatingpositioning mechanism for the floating plate heater 16 spacing theheater element just below the water surface 14 so that there issufficient contact with the water to cause vaporization. In analternative embodiment shown in FIG. 7, the floating heater plate islocated in a shallow bath that also floats at the water surface 14 ofthe body of water 13. In this embodiment the floating plate heatercomprises at least one aperture to allow water to fill the bath to coverthe heater plate 16. The small volume of water in the bath is rapidlyheated to produce vapor.

FIG. 4-B shows another embodiment where the plate form is rippled ordimpled in a regular or irregular fashion. The rippling and/or dimplingprovides valleys which allow pockets of water to accumulate on the uppersurface of the floating plate heater 16. In this embodiment, thefloating plate heater 16 is naturally buoyant, so it can float withoutthe need for a support grid or other buoyancy device.

FIG. 4-C illustrates a flexible tape heater 3 which has been wound intoa helix. In this embodiment the floating, helical flexible tape heater17 can intrinsically float such that a sufficient portion of thefloating, helical flexible tape heater 17 is immersed in the body ofwater 13. In another embodiment the flexible tape heater 3 could bewound in a horizontal spiral, FIG. 4-D. For both the FIGS. 4-C and 4-Dembodiments a support grid 15 as used in FIG. 4-A may be used toposition the flexible tape heaters 3, 12, 17.

The preceding embodiments for the floating heater 3, 12, 16, 17represent a number of defined configurations whereas in use the floatingheater may assume a combination of the defined or undefinedconfigurations. For example a long helix which continues as a spiral,combining FIGS. 4-C and 4-D.

In the above embodiments of the floating heater 3, 12, 16, 17 the heaterprovides effective heat transfer to the water surrounding the heater. Inaddition, the water adjacent to the water surface is heated forvaporization rather than heating the whole body of water from the bottomup as in the case of a heater being located at the bottom of the body ofwater 13.

Additionally, the flexible tape heater formation may be spiraled orotherwise formed so as to be partly immersed in the body of water 13 sothat it heats both the water near the air and the air near the water toproduce a stratified zone of heat to improve water uptake forhumidification. Thus, the floating heater 3, 12, 16, 17 may be morepower efficient in generating water vapor, and more effective in quicklyachieving the desired water surface temperature for humidification atstart-up of the apparatus.

Multiple Zone Heating

FIG. 5 illustrates a respiratory apparatus which makes use of threeheaters that are of the same general construction and use as describedfor the flexible tape heater 3 and the floating plate heater 12, 16, 17described above.

The heaters may comprise multiple heating circuits, so that each of thethree heater zones may be operated independently.

A flow generator 20 or blower supplies gas supplied from an ambienttemperature supply which may be the air in the room or augmented orreplaced by a specific gas supply such as oxygen. A pre-heater 18 islocated in the blower coupling 10 leading to the humidifier 1. Theblower coupling may be rigid, flexible or a conduit as required for theoperation of the blower coupling 10 or the operation of the pre-heater18 located within the blower coupling 10. The pre-heater 18 is connectedto the controller/power supply 21, of the base unit 22, which suppliespower and communication with any sensing or controlling components 7 ofthe pre-heater 18, as per the flexible tape heater 3 embodiment. Thepre-heater 18 is connected to the floating heater 12, 16, 17 of thehumidification chamber 1 at the blower conduit connector end 11. Thefloating heater 12, 16, 17 receives the controller/power supply 21 powersupply and any communication, with the sensing or controlling components7 of the floating heater 12, 16, 17, via the pre-heater 18.

Alternatively the floating heater 12, 16, 17 may also connect with thecontroller/power supply 21 via the wall of the blower coupling 10 in themanner described above in relation to FIGS. 6-A and 6-B discussing thepatient conduit 4.

The post heater 19 is located in the patient conduit 4. The patientconduit connector end 2 provides the controller/power supply 21 powersupply and communication for the sensing and controlling components 7 ofthe post heater 19. The patient conduit connector end 2 may connect tothe controller/power supply 21 via floating heater 12, 16, 17 as shownin FIG. 5 or via the conduit wall 25, as shown in FIGS. 6-A and 6-B, andthen via the humidification chamber 1 to the controller/power supply 21in the base unit 22.

In an alternative embodiment one or more of the heaters may not be ofthe type described above but another suitable heating element. Forexample, the pre-heater 18 may be formed as a simple wire heater orother conventional heater type rather than as a flexible tape heater ofthe type described herein.

The use of such arrangements may give the advantages of:

A single inter-connected heater system which is internal to the blowercoupling 10, humidification chamber 1 and patient conduit 4;

The complete heater, sensor and control system can be removed simply forcleaning, maintenance or replacement;

The interconnection facilitates a high degree of closed loop control fortemperature and humidity of the gas delivered to the patient;

The ability to sense temperature and humidity at different sections ofthe patient conduit 4 in order to control the condensation at varioussections in the patient conduit 4;

The different components of the heater and/or sensing/control system maybe used in combination or separately within a conventional humidifier.For example the flexible heating tape 3 may also be used to heat thepatient conduit 4 together with a conventional humidifier with a heatingbase plate. Alternatively the floating heater 12, 16, 17 or flexibletape heater 3 may be used to heat the body of water 13 in thehumidification chamber 1 together with a heated or insulated wallpatient conduit 4, as described above; and/or

The ability to install multiple heaters in parallel and series at anylocation of the respiratory apparatus. This may allow, for example,“super heating” during the beginning operation of the respiratoryapparatus when the body of water 13 requires time to reach the desiredtemperature. The temporary extra heating of the air with multiple heatercircuits would increase the capacity of the air to take up the coolerwater. This may be controlled or profiled in response to the temperatureof the water in the body of water 14 to provide the appropriate level ofhumidity.

For the respiratory apparatus the placement of the three heaters, andthe timing and sequence of their use allows the gas comfort features oftemperature and humidity to be managed by allowing the separate,staggered production of:

Heating of an ambient gas that has a low absolute humidity;

Water vaporization; and/or

Heating of the gas that has an increased absolute humidity (after thehumidification chamber 1).

The following example of use illustrates an advantage in the operationof the sample embodiments described herein.

Patient respiratory gas requires attention to the comfort features oftemperature and humidity, in particular in winter and colder climates.In the embodiments, the aim of the system from a cold start-up is torapidly deliver warm gas initially and then increase humidity over timeas the humidifier warms up. This approach allows the patient to receivecomfortable warm air closely followed by an increasing relativehumidity, before there is an onset of any adverse symptoms of lowhumidity respiratory assistance.

For a cold start in a winter climate the three heater system may thusoperate in the following manner. Firstly, the cool ambient temperaturegas from the flow generator 20 is warmed by using the pre-heater 18 inthe blower coupling 10 with perhaps assistance from the post-heater 19in the patient conduit 4. This initially provides warm, dry air to thepatient.

As the warmed gas flow begins to absorb appreciable water vapor from theunheated water in the humidification chamber 1, the post-heater 19 inthe patient conduit 4 would begin or increase its heating in order toprevent “rain-out” condensation in the patient conduit 4. The initialwarming of the air with the pre-heater 18 has the advantage ofimmediately commencing a degree of humidification, as a simple“pass-over” operation, while the floating heater 12, 16, 17 is stillwarming up the water. The heat for vaporization in the simple“pass-over” operation being provided by the heated air.

As the floating heater 12, 16, 17 begins to warm the water surface andrapidly increase the absolute humidity in the gas passing through thehumidification chamber to achieve the desired level of humidification,the post-heater 19 in the patient conduit 4 would adjust its heating tomaintain the absolute humidity by preventing condensation in the patientconduit 4. The post-heater 19 may also serve to maintain the desired gastemperature in the patient conduit 4. The pre-heater 18 may have aheating profile based on the level of heating of the body of water 13 inthe humidification chamber 1, the heating profile being the rate ofheating of the gas flow in a period of time that can be provided bychanging the power to the pre-heater 18 or the structural configurationof the pre-heater 18. It is believed that there may be more effectiveand control of the humidity by controlling the air temperature asopposed to heating the water.

An additional advantage of this sample embodiment is that it allowsreduced power consumption at humidification start up so that therespiratory apparatus may be able to be operated by direct current powersupply or a portable power supply. Also, satisfactory operation canstill be obtained when two or more heaters are multiplexed, one heateris operated at a time but there is cycling in operation between two ormore heaters.

Inlet Conduit Connection

Referring to FIG. 8, the power supply/controller 21 may be connected tothe inlet conduit/blower coupling 10 by a connector 52. The connector 52has a first connector 52 a connected to the power supply/controller 21and a second connector end 52 b connected to the inlet conduit 10. Theinlet conduit 10 has a flow generator cuff or connector 54. The flowgenerator cuff 54 has an end 54 a which is configured for connectionwith the flow generator 20. The flow generator cuff 54 also has anovermolded grip or cuff 54 b which defines a terminal clip 54 c.

As shown in FIG. 9, the inlet conduit 10 is connected to the flowgenerator 20 by the flow generator cuff 54. The connector 52 isconnected to the flow generator cuff 54 at the terminal clip 54 c.Although not shown in FIG. 9, it should be appreciated that the firstend 52 a of the connector 52 is connected to the power supply/controller21. The power supply/controller 21 provides electrical current andsignals to the flow generator cuff 54 through the connector 52.

Patient Conduit Connection

The patient conduit/air delivery hose 4 is connected to the patientinterface 5 by a mask connector or cuff 56, as shown in FIG. 10. Thepatient conduit 4 includes a tube 4 a, for example of thermoplasticelastomer, and a helical rib 4 b of very low density polyethylene. Wires4 c, 4 d, 4 e are supported in the helical rib 4 b so as to be incontact with the outer surface of the tube 4 a. The wires 4 c, 4 d, 4 emay be used to heat the tube 4 a and to carry signals to and from thepower supply/controller 21. It should be appreciated that the inletconduit 10 may have a construction similar to the patient conduit 4,including a tube 10 a, a helical rib 10 b, and wires 10 c-10 e supportedby the helical rib on the tube.

Inlet Conduit and Flow Generator Connector Cuff

Referring to FIG. 11, the flow generator cuff 54 includes a connectorblock 54 a. A grip or cuff 54 b is overmolded on the connector block 54a to connect the connector block 54 a to the inlet conduit 10. Theovermolded grip or cuff 54 b includes grip features 54 d, such asrecesses for a user's fingers, in the outer surface of the overmoldedgrip or cuff 54 b to provide a better grip on the connector cuff 54.

As shown in FIGS. 8, 12 and 13, the flow generator cuff 54 includes aterminal clip 54 c that receives the second connector end 52 b of theconnector 52. As shown in FIG. 13, the terminal clip 54 c includes a rib54 n that is received in a lead-in 52 e of the connector 52. The rib 54n engages the lead-in 52 e to secure the connector 52 to the terminalclip 54 c.

The terminal clip 54 c also includes a tooth 54 e that locates the wires10 c, 10 d, 10 e of the inlet conduit 10. The wires 10 c, 10 d, 10 e areplaced on the outer surface of the thermoplastic elastomer tube 10 a andheld in place on the outer surface by the helical rib 10 b.

A channel 54 j is provided in the connector block 54 a to allow theovermolded material 54 b to flow and bond to the inside of the tube 10 ato establish the connection between the connector block 54 a and theinlet conduit 10. The connector block 54, the tube 10 a and theovermolded material 54 b may be formed of materials that will chemicallybond.

Referring to FIG. 14, the terminal clip 54 c includes terminal clip pins54 h that are received in hinged slots 54 g of a terminal clip hinge 54f. The terminal clip hinge 54 f is provided on the connector block 54 a.The terminal clip 54 c is snap-fit into the terminal clip hinge 54 f toensure connection of the tooth 54 e with the wires 10 c, 10 d, 10 e ofthe inlet conduit 10. As shown in FIG. 15, the terminal clip 54 c may beattached to the connector block 54 a prior to attachment of the inletconduit 10 to the connector block 54 a. The terminal clip pins 54 h areattached in the hinge slots 54 g and the terminal clip 54 c is tilted orrotated forward. The inlet conduit 10 is then attached to the connectorblock 54 a and the terminal clip 54 c is then rotated or pivoted back sothat the tooth 54 e contacts the wires 10 c, 10 d, 10 e of the inletconduit 10. As shown in FIGS. 16 and 17, the connector block 54 aincludes a guide away 54 p for the helical rib 10 b of the inlet conduit10 to position the wires 10 c, 10 d and 10 e for contacting by the tooth54 e.

Referring to FIG. 17 the terminal clip 54 c includes an arched portion54 k that defines a channel with the guide way 54 p (FIG. 16) when theterminal clip 54 c is inserted into the terminal clip hinge 54 f. Agroove 54 i (FIG. 18) is provided in the connector block 54 a to receivethe helical rib 10 b and the wires 10 c, 10 d, 10 e of the inlet conduit10. The groove 54 i has a smooth surface and wide contact area toprevent or minimize damage to the wires 10 c, 10 d, 10 e. As also shownin FIG. 18, a void 54 m is provided adjacent to the channel 54 j toallow for the passage of any air during the overmolding of the grip orcuff 54 b to the connector block 54 a.

Referring to FIGS. 19-21, the second connector end 52 b has a gripfeature 52 c to permit easier gripping of the second connector end 52 b.Strain relief features 52 d are also formed in the second connector end52 b to increase flexibility. The grip and strain relief features mayalso be provided to the first connector end 52 a of the connector 52.

Contacts 52 f, 52 g, 52 h are provided for sending and receiving signalsfrom the wires 10 c, 10 d, 10 e of the inlet conduit 10. Although theinlet conduit 10 is shown as including three wires and a terminal clip54 c is shown as having three terminals for receipt of the threecontacts of the second connector end 52 a, it should be appreciated thatany number of wires, terminals and contacts may be used for the deliveryand receipt of signals from the power supply/controller 21 to the inletconduit 10.

Patient Conduit and Mask Connector Cuff

Referring to FIGS. 22-34, a mask connector or cuff 56 is provided forthe connection of the patient conduit/air delivery hose 4 to the patientinterface 5. The mask connector or cuff 56 includes a connector block 56a that is connected to the patient conduit 4 by an overmolded grip orcuff 56 b. The connector block 56 a, the tube 4 a and the overmoldedcuff 56 b may be formed of materials that will chemically bond.

As shown in FIG. 24, the connector block 56 a is connected to an inlet 5a of the patient interface 5. The inlet 5 a may be, for example, theswivel elbow of a mask.

A printed circuit board (PCB) 56 c is provided around the outer surfaceof the connector block 56 a. The wires 4 c, 4 d, 4 e of the patientconduit 4 are attached to the PCB 56 c. As shown in FIGS. 25, 27 and 28,the connector block 56 a includes snaps or pins 56 i that engage holesor apertures 56 u in the PCB 56 c. The PCB 56 c is thus wrapped aroundan outer surface of the connector block 56 a and held in place. Athermal fuse 56 d and a temperature sensor 56 e, for example athermistor, are provided on the PCB 56 c. As shown in FIGS. 23 and 26,one or more windows 56 j are provided in the outer surface of theconnector block 56 a where the thermal fuse 56 d and the temperaturesensor 56 e are provided. The windows 56 j are covered by the PCB 56 c,as shown in FIG. 24. As discussed in more detail below, the PCB 56 cincludes a heater track that is cooled by exposure of the PCB 56 c tothe airflow along the window 56 j.

A helical rib 56 f is provided on the outer surface of the connectorblock 56 a to locate the patient conduit 4, as shown in FIGS. 22-26. Asshown in FIG. 25, the outer surface of the connector block 56 a includesa stepped recess 56 h to allow the overmold material to flow and bond tothe underside of the flexible PCB 56 c. As shown in FIG. 29, theconnector block 56 a also includes a channel 56 t to allow the overmoldmaterial to bond with the inside of the tube 4 a of the patient conduit4. Referring back to FIG. 25, a void 56 g is provided adjacent thechannel 56 t to allow for the escape of air during overmolding. As alsoshown in FIGS. 28 and 29, the end of the connector block 56 a includes aprofile 56 n that minimizes the capacity for debris to collect and to becleaned if debris does collect. The end of profile 56 n also minimizesflow impedance of the overmolded material.

As shown in FIGS. 25 and 27, an access channel 56 m is provided betweenthe helical rib 56 f and the end channel 56 t to allow the overmoldmaterial to bond the tube 4 a to the connector block 56 a. As shown inFIG. 30, the tube 4 a is twisted on to the connector block 56 a and thewires 4 c, 4 d, 4 e of the patient conduit 4 are soldered to theflexible PCB 56 c as shown at 56 p.

Referring to FIG. 31, the overmolded grip or cuff 56 b may include amolded grip feature 56 q, such as recesses to accommodate a user'sfingers, to improve the gripping ability of the mask cuff or connector56. The connector block 56 a may be formed of a rigid polymer and theovermolded grip or cuff 56 may be formed of a thermoplastic elastomer.As shown in FIG. 32, the connector block 56 a may have a standard 22 mmISO taper for connection to the patient interface. As also shown in FIG.32, the overmolded material may be blanked off at 56 s in the region ofthe thermal fuse 56 d.

Referring to FIGS. 33 and 34, the circuit on the flexible PCB 56 cincludes the thermal fuse or switch 56 d and the thermal sensor 56 e.One of the wires, e.g. 4 c, may be used as a temperature sensing wirefor sending a temperature signal to the power supply/controller 21. Theother wires, e.g. 4 d, 4 e, may be used as heater wires to heat the tube4 a of the patient conduit 4. If the temperature exceeds a certainvalue, the thermal fuse 56 d is configured to cut off current to theheater wires 4 d, 4 e.

The flexible PCB 56 c and temperature sensor 56 e and thermal fuse 56 dshould be provided on the connector block 56 a as close to the inlet 5 aof the patient interface 5 and the air path through the patient conduit4 as possible. The mask connector or cuff 56 should also be formed assmall as possible to permit its use with existing breathing apparatus.The use of the overmolded grip or cuff 56 b is also useful for securingthe patient conduit 4 to the connector block 56 a and to secure theflexible PCB 56 c, including the temperature sensor 56 e and the thermalfuse 56 d in place. The use of the overmolded material also helps toreduce or eliminate any locations where bacteria could grow.

The mask connector or cuff 56 as described herein is formed ofbiocompatible materials. The connector block 56 a also includes an end56 r (FIG. 32) that includes a standard 22 mm female ISO taper for usewith existing patient interfaces. The use of the overmolded materialalso eases manufacture and improves reliability of the mask connector orcuff.

Power Supply/Controller

Referring to FIG. 35, the power supply/controller 21 comprises a switchmode power supply 21 a, a switch 21 b, a control unit 21 c, and aplurality of LED's 21 d. The power supply/controller 21 has an AC powerinput 21 e, a DC power output 21 f, and a bypass AC power lead 21 g tothe flow generator 20. The AC power input 21 e may be, for example,110-240V AC universal inputs. The switch 21 b may be a MOSFET switch inseries with the heater element controlled by the control unit 21 c. TheDC power output 21 f may be, for example, a 500 mA regulated 5V DC, or a1.3 A, 24V DC output. At 24V the power output is 30 W.

The power input 21 e is connected to the switch mode power supply 21 aand the bypass 21 g is connected to an AC power socket of the flowgenerator 20. The power supply/controller 21 is configured to providepower to the inlet conduit 10, regulate preset temperature levels at thepatient interface 5, and act as an ON/OFF control.

The control unit 21 c is a closed loop temperature control system. Thetemperature sensor 56 e located in the mask cuff 56 provides thefeedback signal through the wire 4 c of the patient conduit 4 back tothe control unit 21 c. It should be appreciated, however, that thecontrol may not rely on a feedback of a temperature signal. The controlunit 21 c may instead be configured to provide a predetermined amount ofpower to the output 21 f without reliance, or dependence, on atemperature sensor signal.

The DC power output 21 f supplies power to the inlet conduit 10 and theswitch 21 b is provided in series with the power output 21 f and iscontrolled by the control unit 21 c. The power regulation is based on anON/OFF control technique. The power regulation has fixed duty cycles ata rate of about 95-99%. The OFF cycle, at a rate of about, for example1-5%, is used for temperature sensing.

The LEDs 21 d may include a green LED to indicate that power is on andbeing supplied to the inlet conduit 10. An amber LED may be provided toindicate that the power output 21 f is ON, but not provided to the inletconduit 10. A red LED may be provided to indicate a fault. Further LEDsmay also be provided for indicating and/or controlling the temperature.Manually operable buttons (not shown) may be provided to the powersupply/controller to allow control of the temperature by a patient orclinician in response to an indication of temperature by the LED's.

The control unit 21 c is configured to produce a fixed power switchingfrequency and duty cycles for the power output 21 f to heat the inletconduit 10. The control unit 21 c is also configured to sense thetemperature via the signal sent by the temperature sensor 56 e throughwire 4 c. Based on the sensed temperature, the control unit 21 c isconfigured to regulate the temperature to a preset temperature whenambient temperature changes. The control unit 21 c is further configuredto record the preset temperature when the power control/supply 21 isturned off.

The control unit 21 c may also latch a fault state when a fault isdetected, and clear the fault by recycling power. If a fault occurs afault detection circuit locks into a fault condition to send a faultsignal to a driver block (FIG. 37a ) the fault will continue until thepower is turned OFF and ON again. The control unit 21 c may beconfigured to detect faults, including any discontinuities in the wires4 c-4 e and 10 c-10 e, any arcing and/or bad connections in the flowgenerator cuff 54 and/or the mask cuff 56. The control unit 21 c mayalso detect low voltage.

The power output 21 f is maintained in the OFF state by the control unit21 c when a fault is detected and is maintained in the OFF state untilthe power is recycled and the fault state is cleared.

The status of the power supply/controller 21 may be indicated throughthe LEDs 21 d.

As shown, for example in FIGS. 5 and 8, the power supply/controller 21may be separate from the flow generator 20 and the humidifier. There isno information exchange between the flow generator 20 and the humidifierand the closed loop control does not include control based on airflowrate, humidity level, and humidifier outlet temperature, for example. Itshould be appreciated, however, that information may be exchanged, forexample through the sensing wire 4 c. The control described aboveprevents “rain out” in the patient conduit 4 and delivers the humidifiedair to the patient interface 5.

It should be appreciated that the power supply/controller 21 may beintegrated with the flow generator 20 or the humidifier control system.Information may be provided to the integrated power supply/controllerregarding the operation of the flow generator, the humidifier, andambient air. By integrating the power supply/controller with the flowgenerator 20 or the humidifier, the system will be more able to controlthe temperature at the patient interface 5, the humidity levels and“rain out” at a wider range of ambient temperature and humidities.

Referring to FIG. 36, a three wire heated tube or conduit according to asample embodiment of the invention is illustrated. The wires 4 d, 4 emay be formed, for example, from a 25 m long wire having a diameter of0.23 mm, and be formed, for example, of copper. The sensing wire 4 c maybe connected to the heating wires 4 d, 4 e at a connection point 4 fthat is approximately the middle of the wire forming the wires 4 d, 4 eand divides the wire into two resistances Ra, Rb. The total resistanceRa+Rb may be equal to about 15-21Ω, for example about 18Ω, at 20°-26°C., for example about 23° C. The total resistance Ra+Rb is about 18Ω,and about 21Ω, when the wire resistors are heated up to about 33° C.using a 24V DC supply at a power of about 30 W. As discussed above, theDC voltage V+ may be supplied across J1 and J3 at a duty cycle of, forexample, about 95-99%. The resistances Ra, Rb generate heat during theflow of current through the wires 4 d, 4 e to heat the conduit 4. Thesensing voltage Vsen may be determined during the 1-5% OFF cycle. Duringthe OFF cycle, the switch 21 b is activated by the control unit 21 c toswitch the system into a sensing state and sensing current from J1passes resistance Ra and resistance RT1 of the temperatures sensor 56 eback to J2. The resistance RT1 of temperature sensor 56 e may be about1-50 kΩ and resistance Rb may be about half of Ra+Rb, or about 5-15Ω,for example about 10Ω, so Rb is omitted.

Although the sensing wire 4 c is disclosed as being connected to thetemperature sensor 56 e, it should be appreciated that the sensing wiremay be connected to a different sensor, such as a pressure sensor, forexample in the event that the control is not a feedback control based onthe detected temperature.

The fuse F2 of the thermal circuit 56 d is thermally coupled to theheater track of the PCB 56 c. The PCB 56 c may be, for example, about0.05-0.15 mm thick, for example about 0.1 mm thick, have a resistance ofabout 0.05-0.15Ω, for example about 0.1Ω, and a power output of about0.12-0.24 W, for example about 0.18 W. As discussed above, one side ofthe PCB 56 c faces the open window 56 j so the PCB 56 c contacts the airin the patient conduit 4. The air flowing in the conduit therefore coolsthe PCB 56 c to just above the temperature of the air in the conduit. Ifthe flow generator stops, or the air flow through the conduit isblocked, the temperature of the PCB 56 c will rise and trip the fuse F2to protect the patient conduit 4 from damage. The temperature sensor 56e and the fuse F2 of the thermal circuit 56 d thus provide over airtemperature protection, tube over heating protection, and low airflowprotection. The thermal circuit 56 d may include a thermostat, forexample a bi-metal strip, instead of the fuse, and an increase inimpedance of the thermostat would act to suppress, or stop, an increasein the current.

As the patient conduit 4 delivers the humidified air to the patientinterface 5, the power supply/controller 21, the mask cuff 56 and itscomponents, and the patient conduit 4 should comply with safetystandards for temperature regulation, for example, ISO 8185. Undernormal operating conditions, the patient or clinician should be able toset the temperature of the air delivered to the patient interface 5 fromambient to about 30° C. If no alarm system or indicator is provided tothe system, in accordance with ISO 8185, sections 51.61-51.8, undernormal and single fault conditions, the temperature of the air deliveredto the patient interface 5 should not exceed about 40°-42° C., forexample about 41° C. This maximum temperature (e.g. 41° C.) is under themaximum energy level of 43° C. at 100% RH. The fuse F2 of the thermalcircuit 56 d may be chosen to trip off at the maximum temperature.

Referring again to FIG. 36, the three wire (4 c-4 e) electrical circuitof the patient conduit 4 includes the heating elements Ra, Rb in serieswith the heater track and fuse F2 of the PCB 56 c, the wire 4 c forsupplying the sensing voltage Vsen, and the thermal sensor 56 eincluding the thermal resistor TR1 attached to the middle 4 f of the ofthe heater wires 4 d, 4 e. The electrical circuit has two states: ON andOFF. In the ON state, also referred to as the heating state, the wire 4d is connected at J1 to the voltage V+, for example the 24V DC from thepower output 21 f. The heating current flows through J3, wires 4 d, 4 e,J4 and the switch 21 b and into ground GND. In the ON state, the sensingvoltage Vsen at J2 will not sense the air temperature, but will senseabout half of voltage V+, e.g. about 12V.

In the OFF state, the switch 21 b is switched off and the heater wires 4d, 4 e will be pulled up by V+, e.g. about 24V, and the sensing currentpasses through J1, Ra, RT1 and back to J2.

The power supply/controller 21 may include circuits for performingnumerous functions. These circuits may include: 1) a power switchingcontrol circuit; 2) a tube interface and gate drive circuit (driverblock); 3) a fault detection and latching circuit (fault detectionlatch); 4) a temperature preset/control circuit; and 5) a start up andindication circuit.

Power Supply/Controller Circuits

A sample embodiment of the circuits of the power supply/controller 21 isshown in FIG. 37a . The circuit includes a temperature control circuitconfigured to control the temperature of the heated conduit(s), a faultdetection latch, a sensing circuit and a driver block. The driver blockis connected to the switch 21 b, which may be a MOSFET.

Referring to FIGS. 37b -1-37 b-4, a sample embodiment of the circuit ofFIG. 37a may be based on, for example, an UC2843 control IC, availablefrom Texas Instruments. It should be appreciated that other controlcircuits may be used. The power switching control circuit has chipover-current and over-voltage protections which can be used for errorhandling. The power switching control circuit may also have an RC clockand under-voltage lockup and a push-pull output driver. By setting theoscillating RC clock such that R12=22,000Ω and C5=330 nF, the switchfrequency may be set at 138 Hz. The time period for such a frequency isdetermined by T=R12×C15 (22,000×0.00000033)=7.26 mS. By ratio of R12 andC5, the power switching control circuit provides a 100 μS OFF period,and the duty cycle is thus 100 μS/7.26 mS=1.38%.

At normal heating conditions, the power switching control circuit ofFIGS. 37b -1-37 b-4 drives the transistor gate of the switch 21 b atabout 98.62% duty cycles. The ON state of the circuit cannot beinterrupted by Vfb signals. At the Vfb critical point, the gate signalcan be shown as 50% 69 Hz outputs.

The power switching control circuit has enable input through the Vfbpin. When any of the signals through D3 and D4 to low, it will disablethe output of the switch 21 c. The sensing current Isen is not used forthis application as R10 and R20 set the sensing voltage Vsen below 1V.

Referring again to FIGS. 37a and 37b -1-37 b-4, the sensing voltage Vsenhas two functions: 1) when the heater power is ON, the sensing voltageVsen detects the heater wires continuity, or any arcing or badconnections by sensing middle voltage V+; and 2) when the heater poweris OFF, the sensing voltage Vsen senses the air temperature via the RT1and R13 divider voltages. The Q2, Q3 network provides right logic forsensing operations and MOSFET Q3 provides low impedance (Rdson) fortemperature sensing. Q4 MOSFET gate drives network R23, R25 limiting themaximum gate voltage; R24 and D5 together with R23 control the Q4 switchoff speed.

The fault detection circuit operates when heater power is ON. The Vsensignal is fed into a window comparator, for example an ultra-power quadcomparator, such as the LP339AM, available from National Semiconductor.U6B, U6D; R31, R36 and R43 divider provide a +/−2V window voltage at 12Volt; the output of window comparator signals will feed into secondstage of the comparator U6C.

The second stage of comparator samples the Q4 gate signal as a base lineand detecting the error signal from window comparator output. Whensystem has no fault detected, window comparator outputs as highimpedance, R34 and R40 divider has higher voltage out then invertingcomparator input R33 and R42 divider network, U6C will output high.

When the system has a fault detected, window comparator outputs low, R34and R40//R35 divider has lower voltage then inverting comparator inputR33 and R42 divider network, U6C will output low to U2A latch CLR pin.

When latch CLR pin 1 receives a low signal the Q pin 5 will output alatched fault signal, it will kill the U3 output switching signals. Thelatch may be, for example, a 74HCT74D U2A from Fairchild Semiconductor.

The temperature sensing operation is only performed during the power OFFperiod. The air temperature sensor RT1 and divider base resistor R13provides the temperature information Vsen, it directly feed into thecomparator U6A inverting input, a potentiometer and it's network doesthe temperature preset function. The output of this comparator drives D4and controls the U3 switch output.

The start up circuit provides a 140 mS delay when system start up and itwill reset the latch. After reset, the system will at ON state. Thestart up circuit may be, for example, an IC U4 TCM809, available fromTelCom Semiconductor, Inc.

The accuracy of temperature measurement is based on two parts: 1)sensing accuracy; and 2) accuracy of reference. Sensing accuracy dependson NTC thermistor RT1 and series resistor R13. For example, a good NTCsensor RT1 may have up to a 1-5%, for example about 3%, accuracytolerance; the series resistor R13 may have up to a 0.5-1.5% tolerance,for example about a 1% tolerance. The accuracy of the temperature presetcircuit is determined when the port is at highest setting (30° C.). Theport resistor is 0Ω and the accuracy is dependent on the 1% resistornetwork. However, when the port is set to the lowest setting, 20% of theport resistor tolerance will be added in.

The conduits 4 and 10 will overheat when there is no gas flow in thetubes. The heat can be accumulated in the tube, if the tube is covered,for example under a quilt, and the heater element temperature can riseto 120-150° C. The heat can accrue when the thermal switch is exposed incold air, but part of the tube was covered, for example under the quilt.For this reason, a no flow or low flow signal from the flow generatorshould able to trip off the heated tube power supply.

A three way connector is provided between thermistor sensor RT1 and thecontrol unit 21 c. Any bad connection on the contactor will causeincreasing impedance on the sensing circuit; for NTC thermistor RT1 itwill lower the temperature readings, and it can cause air temperaturerise and may trip the thermal switch 21 b at the tube.

There are two ways to solve fault states in the temperature sensing. Afirst way is to change the voltage divider logics, as contact resistanceis high the air temperature goes low. The other way to protect thesensing contactor is to off-set the sensing wire by changing R6 and R31to 8.2 kΩ This offset reference voltage can detect the high impedanceconnectors.

Cuff Configurations

As shown in FIGS. 38-40, the configuration of the inlet conduitconnector cuff and/or the patient conduit and mask connector cuff maytake various forms. Each of the mask connector or cuff configurationsshown and described herein may include grip features, and sufficientstrain relief features to improve the flexibility of the connector orcuff.

Tube Configurations

Referring to FIG. 41, the inlet conduit 10 and/or the patient conduit 4may include an inner tube 4 a, 10 a, a helical rib 4 b, 10 b, and anouter tube 4 f, 10 f. The outer tube 4 f, 10 f may be formed of the samematerial as the inner tube 4 a, 10 a. The outer tube 4 f, 10 f may alsobe provided with a fleece or flocked material to improve the feel and/orgrip of the conduit, and/or to improve the thermal insulation propertiesof the tube and/or the visual appeal. If the outer tube 4 f, 10 f is notprovided, the outer surfaces of the inner tube 4 a, 10 a and the helicalrib 4 b, 10 b may be provided with a fleece or flocked material forsimilar reasons.

Referring to FIG. 42, the inlet conduit 10 and/or the patient conduit 4may include an inner tube 4 a, 10 a and an outer tube 4 f, 10 f spacedby corrugations 4 g, 10 g. The corrugations 4 g, 10 g may extend axiallyalong the conduit 4, 10, or may extend helically along the conduit 4,10. Wires may be provided within the corrugations 4 g, 10 g, between theinner tube 4 a, 10 a and the outer tube 4 f, 10 f. The corrugations mayalso be used to provide a supplemental gas flow along the conduit 4, 10,or to provide a flow of liquid, for example water, to regulate thetemperature of the gas flow in the conduit 4, 10. The corrugations mayalso be used to exhaust gas, for example from the patient's exhalation,from the patient interface. The outer tube 4 f, 10 f may also be coveredin fleece or flocked material.

Patient Conduit, Mask Connector Cuff, and Flexible Circuit

Referring to FIG. 43, a patient conduit 400, mask connector cuff 560 andflexible circuit 570 according to another sample embodiment areillustrated. The patient conduit 400 is connected to the mask cuff 560by an overmold material 580 that encompasses the flexible circuit 570.The overmold material 580 is overmolded onto the patient conduit 400 andthe mask cuff 560. The flexible circuit 570 may include the tube wires,sensors, fuses and other components described above in relation to theother sample embodiments.

The mask cuff 560 may be formed as a separate part that is connected tothe patient conduit 400 through the overmold material 580.Alternatively, the mask cuff 560 may be formed as a single piece withthe overmold material 580.

Although the invention has been herein shown and described in what isconceived to be the most practical and preferred embodiments, it isrecognized that departures can be made within the scope of theinvention, which is not to be limited to the details described hereinbut is to embrace any and all equivalent assemblies, devices andapparatus. For example, the heating wires may be PTC elements with avoltage regulation to limit the temperature of the wires ad/or the airin the conduit(s). As another example, one or more PTC or NTC wires maybe used in conduction with a resistor to limit the temperature of thewires and the air. As a further example, NTC wires may be used with acurrent regulator, or a measure resistance, to limit the temperature ofthe heating wires. The temperature sensing and heating may also beperformed using only two wires.

In this specification, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise,” “comprised” and “comprises” where they appear.

It will further be understood that any reference herein to known priorart does not, unless the contrary indication appears, constitute anadmission that such prior art is commonly known by those skilled in theart to which the invention relates.

What is claimed is:
 1. A conduit for use in a respiratory apparatus fordelivering breathable gas to a patient, the conduit comprising: a tube;a helical rib on an outer surface of the tube; at least three wires incontact with the outer surface of the tube and supported between thehelical rib and the outer surface of the tube; a connector connected toan end of the conduit, the connector being configured to be connected toa flow generator or a patient interface of the respiratory apparatus;and a printed circuit board supported on the connector and connected tothe at least three wires, the printed circuit board comprising a thermalfuse and a temperature sensor, wherein one of the at least three wiresis connected to the temperature sensor to provide a signal to a powersupply and controller of the respiratory apparatus and two of the atleast three wires form a heating circuit.
 2. A conduit according toclaim 1, wherein the tube is formed of thermoplastic elastomer.
 3. Aconduit according to claim 1, wherein the helical rib is formed of lowdensity polyethylene.
 4. A conduit according to claim 1, wherein the atleast three wires are copper.
 5. A conduit according to claim 1, whereinthe connector is connected to the conduit by a cuff.
 6. A conduitaccording to claim 5, wherein the cuff is overmolded to the conduit andthe connector.
 7. A conduit according to claim 5, wherein the cuffcovers the printed circuit board.
 8. A conduit according to claim 5,wherein the cuff comprises grip features formed in and/or on an outersurface.
 9. A conduit according to claim 5, wherein the cuff comprisesstrain relief features formed in and/or on an outer surface.
 10. Aconduit according to claim 1, wherein the connector is configured to beconnected to the flow generator and the conduit further comprises aterminal clip configured to be connected to an electrical connector. 11.A conduit according to claim 10, wherein the terminal clip contacts theat least three wires so that power may be delivered to the conduit bythe electrical connector.
 12. A conduit according to claim 10, whereinthe terminal clip is attached to the connector and secured to theconnector by a cuff.
 13. A conduit according to claim 10, wherein theterminal clip comprises at least three terminals corresponding to the atleast three wires.
 14. A conduit according to claim 1, wherein theconnector is configured to be connected to the patient interface.
 15. Aconduit according to claim 14, wherein the connector is configured toconnect to an elbow of the patient interface.
 16. A conduit according toclaim 1, wherein at least one of the at least three wires is connectedto the thermal fuse.
 17. A conduit according to claim 1, wherein thethermal fuse is configured to break the heating circuit if a temperatureof the conduit exceeds a predetermined temperature.
 18. A conduitaccording to claim 1, wherein the connector comprises a windowstructured to expose at least part of the printed circuit board to aflow of gas in the conduit.
 19. A conduit according to claim 1, whereinthe temperature sensor is a thermistor.
 20. A respiratory apparatus fordelivering breathable gas to a patient, comprising: a flow generator togenerate a supply of pressurised gas to be delivered to the patient; ahumidifier to vaporize water and to deliver water vapor to humidify thebreathable gas; a first gas flow path leading from the flow generator tothe humidifier; and a second gas flow path leading from the humidifierto a patient interface, wherein the first gas flow path and/or thesecond gas flow path comprises a conduit according to claim
 1. 21. Arespiratory apparatus according to claim 20, further comprising a powersupply and controller configured to supply and control power to theconduit through an electrical connector.
 22. A respiratory apparatusaccording to claim 21, wherein the power supply and controller comprisesan AC power input connected to a switch mode power supply and a bypassAC power lead connected to the switch mode power supply, and the flowgenerator is connectable to the power supply and controller by thebypass AC power lead.
 23. A respiratory apparatus according to claim 22,wherein the power supply and controller further comprises a control unitconfigured to produce a DC power output from the switch mode powersupply at a selected duty cycle, wherein the DC power output isconnected to the conduit by the electrical connector.
 24. A respiratoryapparatus according to claim 23, wherein the power supply and controllerfurther comprises a switch configured to switch the DC power output onand off at a selected duty cycle.
 25. A respiratory apparatus accordingto claim 24, wherein the control unit is a closed loop temperaturecontrol system and is configured to receive a signal from a temperaturesensor on the conduit during the OFF cycle of the duty cycle and controlthe DC power output to maintain a preset temperature in the conduitduring the ON cycle of the duty cycle.
 26. A respiratory apparatusaccording to claim 23, wherein the control unit is configured to recordtemperature when the power supply and controller is turned off.
 27. Arespiratory apparatus according to claim 23, wherein the power supplyand controller comprises a plurality of LEDs.
 28. A respiratoryapparatus according to claim 27, wherein a first LED is configured toindicate that the DC power output is on and that DC Power is beingprovided to the first gas flow path conduit, a second LED is configuredto indicate that the DC power output is on but that DC Power is notprovided to the first gas flow path conduit, and a third LED isconfigured to indicate a fault.
 29. A respiratory apparatus according toclaim 28, wherein the fault comprises a) a discontinuity in any of theat least three wires of the first gas flow path conduit and the at leastthree wires of the second gas flow path conduit and/or b) arcing and/ora bad connection between the first gas flow path conduit and the flowgenerator and/or between the second gas flow path conduit and thepatient interface and/or c) low voltage.
 30. A method of deliveringbreathable gas to a patient, comprising: delivering a humidified flow ofbreathable gas to a patient interface via a conduit according to claim1; heating the conduit by supplying a DC current at a predetermined dutycycle to a plurality of wires supported by the conduit; sensing atemperature in the conduit during an OFF cycle of the predetermined dutycycle; and controlling the DC current to maintain the temperature in theconduit at a selected temperature.